This invention relates generally to inkjet printers, and more particularly to operations performed by a printhead of an inkjet printer to reduce slew decap effects.
It is generally known that inkjet printers utilize at least one printhead possessing a plurality of nozzles through which ink drops are fired onto a medium, e.g., fabric, paper, etc., to create an image on the medium, e.g., plot, drawing, etc. According to one type of inkjet printer, ink is typically supplied substantially continuously over a plurality of resistors generally located beneath the openings of the nozzles. In use, certain of the resistors are activated, i.e., heated, to vaporize a portion of the ink on the resistors, thereby causing a portion of the ink to be fired through the respective nozzle openings. According to another type of inkjet printer, ink is typically supplied substantially continuously over a plurality of piezoelectric elements located beneath the openings of the nozzles. In this type of printer, certain of the piezoelectric elements are caused to deform at a relatively rapid rate, thereby causing ink positioned thereover to be fired through the respective nozzle openings to produce pixels.
To create an image on the print medium, the printer typically controls the nozzles to produce a pattern of pixels corresponding to the image. The nozzles are generally arranged on one or more printheads that travel back and forth across the surface of the print medium. In this regard, FIG. 1 schematically illustrates a part of a known printer device (e.g., a large format inkjet printer) having an array of printheads 100 in a parallel row. More specifically, FIG. 1 illustrates six printheads 102-112. Each of the printheads 102-112 includes a plurality of printer nozzles (not shown) for firing ink 114, 116 onto a print medium 120. Although FIG. 1 depicts the printer device as having six printheads 102-112, printer devices have been known to possess any number of printheads, e.g., two, four, or more.
The printheads 102-112 are typically constrained to slew back and forth or move in a direction 170 with respect to the print medium 120, e.g., paper, textile, and the like. In addition, the print medium 120 is also constrained to move in a further direction 160. During a normal print operation, the printheads 102-112 are moved into a first position with respect to the print medium 120 and a plurality of ink droplets 114, 116 are fired from the same plurality of printer nozzles contained within each of the printheads 102-112. After completion of a print operation, the printheads 102-112 are moved in a direction 170 toward a second position and another print operation is performed. In a like manner, the printheads 102-112 are repeatedly moved in a direction 170 across the print medium 120 and a print operation is performed after each such movement of the printheads 102-112. When the printheads 102-112 reach an edge of the print medium 120, the print medium is typically moved a short distance in a direction 160, parallel to a main length of the print medium 120, and another print operation is performed. The printheads 102-112 are then moved in a direction 170 back across the print medium 120 and yet another print operation is performed. In this manner, a complete printed page may be produced.
A more detailed description of the printer device illustrated in FIG. 1 may found in commonly assigned application Ser. No. 09/502,667 filed on Feb. 11, 2000, by Xavier Bruch et al., the disclosure of which is hereby incorporated by reference in its entirety.
As the printheads 102-112 move or slew, they create a current of air across the uncapped (or decapped) nozzles of the printheads 102-112. Slew decap is a term of art used to identify this phenomenon in which the current of air causes evaporation of a solvent vehicle component of the ink. In general, evaporation of the solvent vehicle alters the chemical composition of the ink. More particularly, the change in chemical composition results in a less visible drop of ink on the print medium 120. For example, evaporation may cause dye or pigment molecules to move from the nozzle, back into the firing chamber and thus diluting the solvent vehicle. Additionally, the rate of chemical change is relatively greater with lower drop volumes. Thus, as drop volumes generally decrease in order to improve image quality, the effects of slew decap may worsen.
In order to maintain the quality of the printed output, it is generally known to maintain the nozzles in substantially proper operating condition. In this respect, a service station 140 is typically provided along a travel path of the printheads 102-112. The service station 140 is typically configured to maintain the health of the printheads 102-112 by performing servicing operations on the printheads, e.g., a means for wiping, collecting spit ink, capping the nozzles, etc. The service station 140 typically includes a plurality of service station units 142-152 for performing servicing operations on each of the printheads 102-112. Generally speaking, a respective service station unit 142-152 is provided for each of the printheads 102-112. The service station units 142-152 are typically housed within a service station frame 154.
A servicing protocol is typically implemented to control the times and manner in which the printheads 102-112 are serviced. For example, in one respect, if it is detected that certain of the nozzles of the printheads 102-112 have not fired any ink drops for a certain period of time, the printheads are moved to a position over the service station 140 and caused to fire a normally set number of ink drops to thereby clean out the nozzles. In addition, a wiping mechanism positioned in the service station 140 may be caused to wipe excess ink off the nozzles to thereby increase the probability of their proper functionality. In another respect, the protocol may cause the printheads 102-112 to spit a set number of ink drops into the service station after each printing pass in an effort to substantially prevent ink from drying within the nozzles. The servicing protocol typically sets the number of times as well as the frequency of servicing operations based upon a set of normal values which are themselves typically set by the printhead or service station manufacturer. In addition, the normal values of the servicing protocol may vary according to the set printmodes. In general, servicing operations require some time to perform and thus decrease throughput.
The above-described servicing process is generally known as an open loop servicing technique. That is, the servicing protocol that determines when to service the printheads 102-112 as well as the degree of servicing to be applied, takes into consideration certain variables, e.g., time uncapped, drops fired during last printing pass, time in cap, etc. However, these types of servicing protocols typically apply a relatively heavy treatment to greater ensure proper printhead performance regardless of the age of the printheads 102-112. One problem associated with the open loop servicing technique is that ink may be wasted by virtue of spitting more ink drops than is necessary, oftentimes resulting in faster aging of the printheads as well as the service station.
Printer devices have also been known to include a drop detector module 130 operable to detect whether the nozzles of the printheads 102-112 are properly firing ink. In these types of printer devices, servicing operations on the printheads 102-112 may be triggered by detected errors, e.g., clogged nozzles, and a user""s expectations, e.g., desired print quality. It is generally known to position the printheads 102-112 over the service station 140 and spit a certain number of ink drops to clean out the ink in the nozzles. This servicing process is generally known as a closed loop servicing technique. That is, servicing on the printheads 102-112 may occur based upon a closed loop servicing protocol under normal operating conditions, with extra, possibly lighter, servicing operations being performed based upon detected errors, e.g., clogged nozzles. In this regard, the closed loop servicing technique has certain advantages over the open loop servicing technique (e.g., does not waste a relatively large amount of ink, extends the life of the printheads and service station, etc.). However, printer devices that implement the closed loop servicing technique are relatively more expensive and complicated and thus may be unsuitable for certain types of printers (e.g., less expensive printer models).
In addition to the servicing operations, the printing device is generally configured to produce print content (e.g., text, image, etc.) on the print medium in response to receiving a print job. In this regard, the printing device references the print job to produce the print content by generating a plurality of pixels.
While a pixel is often thought of as a physical dot on a print medium, for the purpose of this disclosure, a pixel is defined as a physical dot on a print medium and/or the corresponding logical location utilized by the printing device to determine where the dot should be placed. For example, in response to receiving the print job, the printer determines specific commands. The specific commands may denote each location a pixel is to be positioned on the print medium.
In FIGS. 2A and 2B, there is illustrated a manner in which slew decap may impact a conventional image printing operation 200. As shown in FIG. 2A, a grid 210 depicts a number of greatly magnified logical pixel locations. Within the grid 210, a number of dots 220 depict pixels printed in particular pixel locations. The image the dots 220 form is a plus sign. Due to the fact that the dots 220 are clearly visible and not miss-formed, it is apparent that nozzles used to create the dots 220 have been fired recently enough so that substantially no slew decap effects are evident.
As is shown in FIG. 2B, a grid 230 illustrates the effect of slew decap while printing substantially the same plus sign as depicted in the grid 210. Similarly to the dots 220, a number of dots 240 are shown. Additionally, as illustrated by a number of miss-formed dots 250, sufficient time and/or distance has elapsed to cause slew decap associated problems. For example, as the printhead moved from right to left during the printing of the dots 240 and 250, slew decap occurred in, at least, the one or more nozzles used to create the dots 240 and miss-formed dots 250. Thus, as shown in the grid 230, the image formed by the dots 240 is substantially a minus sign.
Although FIGS. 2A and 2B depict a pixel being produced by a single dot, in a similar manner, pixels formed by a plurality of dots, wherein the plurality of dots are produced by a plurality of nozzles, may also be affected by slew decap. Additionally, while FIG. 2B depicts a miss-formed dot being produced following a period or distance in which no ink was fired, in fact, ink may be fired by one or more printer nozzles other than the printer nozzle used to produce the miss-formed dot without departing from the scope of the invention.
In one respect, the invention pertains to a method for reducing the impact of slew decap on image quality in a printing system. The method includes a printhead. The printhead includes a nozzle and the nozzle is configured to fire ink on a print medium. The ink is operable to produce a pixel on the print medium. The method includes producing a pixel with the nozzle. The pixel is produced by multi-dotting during a single printing pass. Multi-dotting includes firing ink multiple times in succession from the nozzle at a pixel location corresponding to the pixel.
In another respect, the invention pertains to a computer readable medium on which is embedded computer software. The computer software includes a set of instructions for reducing the impact of slew decap on image quality in a printing system includes a printhead. The printhead includes a nozzle and the nozzle is configured to fire ink on a print medium. The ink is operable to produce a pixel on the print medium. The method includes producing a pixel with the nozzle. The pixel is produced by multi-dotting during a single printing pass. Multi-dotting includes firing ink multiple times in succession from the nozzle at a pixel location corresponding to the pixel.
In yet another respect, the invention utilizes an apparatus for operating a printer. The apparatus includes a printhead. The printhead includes a nozzle. The apparatus includes a controller configured to receive a print job and to modify the print job. The modification includes a command to produce a pixel by multi-dotting during a single printing pass. Multi-dotting includes firing ink multiple times in succession from the nozzle at a pixel location corresponding to the pixel. Further, the nozzle is operable to produce the pixel by multi-dotting in response to the modified print job.
In comparison to known prior art, certain embodiments of the invention are capable of achieving certain aspects, including some or all of the following: (1) increase image quality; (2) increase throughput; and (3) save resources. Those skilled in the art will appreciate these and other aspects of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings.